During age-related neurodegeneration, damaged proteins and organelles accumulate within neurons. These proteins and organelles are normally degraded in the lysosomes by cathepsins, which are optimally active at acidic pH. Elevation of lysosomal pH hinders normal degradation within lysosomes and impairs autophagy leading to neuronal dysfunction associated with aging, age-related diseases and lysosomal storage disorders. The molecular processes that regulate lysosomal pH are not clearly understood. In this application, I demonstrate that sAC, a pH-sensitive source of cAMP, is a modulator of lysosomal pH. Genetic or pharmacologic ablation of sAC elevates lysosomal pH leading to accumulation of proteins and autophagosomes both in vitro and in vivo. Thus, sAC is a pH-sensitive regulator of lysosomal pH, defining it as the only known lysosomal pH sensor. The goal of this proposal is to elucidate the mechanism by which sAC regulates lysosomal pH. I propose to test the hypothesis that sAC regulates lysosomal function by regulating trafficking and/or activity of V-ATPase and/or any of the channels and transporters (such as ClC-7) responsible for the counter ion current necessary for lysosomal acidification. I will pursue two Specific Aims: the first aim will elucidate the mechanism by which sAC regulates lysosomal pH in cellular systems. The second aim will investigate the molecular consequences of loss of sAC in vivo by examining whether sAC KO mice exhibit age related progression of lysosomal pathology. The experiments proposed in this application will better our understanding of the mechanism by which lysosomal pH is regulated, which in turn will enhance our understanding of aging, and age-related neurodegeneration and lysosomal storage disorders. If validated this hypothesis will lay the groundwork for future studies examining the particular neuronal deficits caused by sAC disruption, and may identify sAC as a potential target for novel treatment strategies for age-related and genetic neurodegenerative diseases.